A series of experimental investigations is made on the damping capacities of wooden joints under vibration. The experimentally obtained logarithmic decrement λ of bolt-bearing portion of Sugi is about 0. 100. 20 and this value has a tendency to increase according to the stress amplitude. This value is also calculated from the static hysteresis curves of bolt-bearing pressure vs. depression. The logarithmic decrement of wooden beams which contain one lap joint each is O. 0300. 050, which differs little from that of beams without joint. The main reason why is the presense of frictional resistance between two pieces. The logarithmic decrement of a 21. 5m light-framed wooden boat in her two-node vertical vibra-tion is about O. 33, which is resolved into two parts, namely, λ _h , (hydrodynamic damping) and λ _s (structural damping). It is calculated that λ _h =0. 10 and so λ _s =0. 33-0. 10=0.23, which is reasonable comparing to above two basic experiments.